1. Field of the Invention
The present invention relates to a semiconductor light emitting device, a method of manufacturing the same, an image display device, and an electronic apparatus.
2. Description of the Related Art
A semiconductor light emitting device has an active layer operable to generate light, and light generated in the active layer is emitted. Such semiconductor light emitting devices are widely utilized in various technical fields and uses, such as display devices. For instance, starting from a semiconductor light emitting device which has an active layer composed of an AlGaInP compound semiconductor having a wide energy band, light emitting diodes (LEDs) operable to generate light at wavelengths of about 560 to 680 nm can be obtained by changing the crystal mixing ratio in the active layer. This is why the semiconductor light emitting devices are in wide use for display devices such as light emitting diode display devices.
Such a semiconductor light emitting device having the active layer composed of an AlGaInP compound semiconductor, in general, has a structure in which an n-type AlGaInP layer, an undoped active layer and a p-type AlGaInP layer are stacked, and light is generated by injecting a current into the undoped active layer. Incidentally, it may be necessary to form a metallic electrode (n-side electrode) for injecting electrons into the n-type AlGaInP layer, and to form a metallic electrode (p-side electrode) for injecting holes into the p-type AlGaInP layer. Further, there has been known a technology of forming a GaAs layer, for reducing the barrier wall between the electrode and the AlGaInP layer and for obtaining good electrical characteristics. However, the band gap in the GaAs layer is smaller than the band gap in the undoped active layer composed of the AlGaInP compound semiconductor layer, so that the light generated in the active layer would be absorbed by the GaAs layer, resulting in a lowered luminous efficiency.
For solving such a problem and realizing a high luminous efficiency, there has been known a technology of forming a p-type GaP layer, in place of the p-type GaAs layer, between the p-type AlGaInP layer and the p-side electrode (refer to, for example, Japanese Patent Laid-open No. 2008-177393). The GaP layer does not absorb the light generated in the active layer, so that the light can be taken out efficiently.
However, it is difficult to introduce a p-type impurity into the p-type GaP layer in a high concentration. Therefore, it may be necessary, for lowering sheet resistance, to set the thickness of the p-type GaP layer at a value of not less than 10 times the thickness of the p-type GaAs layer. However, it is extremely difficult to etch such a thick p-type GaP layer by wet etching, for manufacturing a semiconductor light emitting device having a minute size, especially a size of less than 1000 μm2.
On the other hand, even in the case of forming the p-type GaAs layer between the p-type AlGaInP layer and the p-side electrode, manufacture of a semiconductor light emitting device having a minute size, particularly, a size of less than 1000 μm2 necessarily results in that the p-type GaAs layer has a reduced size. As a result, the electric resistance of the p-type GaAs layer is raised, and a driving voltage is raised accordingly.
In a method of manufacturing a nitride semiconductor laser device, there may occur a problem in which a top surface (a contact surface for contact with a second electrode) of a second contact layer is contaminated to cause an increase in electric resistance, resulting in a raised operating voltage. In order to obviate such a problem, there has been known a technology for obtaining a nitride semiconductor laser device in which formation of a second contact layer is immediately followed by formation of a second electrode on the second contact layer so that, at the interface of the second contact layer and the second electrode, the second electrode has substantially the same width as the width of the second contact layer, as disclosed in Japanese Patent Laid-open No. 2002-335048. However, the semiconductor laser device disclosed in the patent laid-open document is a nitride semiconductor laser device. Moreover, the document makes no mention of measures to solve the problem encountered in wet etching of a thick p-type GaP layer formed as a contact layer or the problem of a rise in the driving voltage attendant on an increase in the electric resistance of the p-type GaAs layer.
Thus, there is a need for a semiconductor light emitting device and a manufacturing method therefor wherein no problem would occur in processing a semiconductor light emitting device by a wet etching technique and wherein a rise in a driving voltage is obviated. Also, there is a need for an image display device and an electronic apparatus in which such a semiconductor light emitting device is used.